Who is stronger, Cloud or Zack?

[Sephiroth]

Nowadays Cloud's strength is like comparable to Zack's. With his Hero-Strength Increase-Bonus he is above Zack.

And Cloud's character was not destroyed. His "doubts" are always shown in Final Fantasy VII. Cloud does doubt himself even after getting back his true memories. He is only brave when it comes to protecting what is precious to him. And that is what the end of the story shows when the characters leave the Highwind.

Those memories of cloud being killed by the dragon were completely fabricated. Cloud never saw Zack fight a dragon, he filled in the blanks.

No, he didn't do anything. Nothing in the game state that.